1. Double Each Number
Problem:
[1, 2, 3]
Goal:
[2, 4, 6]
Solution:
let arr = [1, 2, 3];
let result = arr.map(num => num * 2);
console.log(result);
2. Get Even Numbers
Problem:
[1,2,3,4,5]
Goal:
[2,4]
Solution:
let arr = [1,2,3,4,5];
let result = arr.filter(num => num % 2 === 0);
console.log(result);
Think: “I want only some values” → use filter()
3. Sum of Numbers
Problem:
[1,2,3,4]
Goal:
10
Solution:
let arr = [1,2,3,4];
let sum = arr.reduce((acc, num) => acc + num, 0);
console.log(sum);
Think: “I want one final value” → use reduce()
4. Convert Numbers to Strings
Problem:
[1, 2, 3]
Goal:
["1", "2", "3"]
Solution:
let arr = [1,2,3];
let result = arr.map(num => num.toString());
console.log(result);
5. Find First Even Number
Problem:
[1,3,5,6,7]
Goal:
6
Solution:
let arr = [1,3,5,6,7];
let result = arr.find(num => num % 2 === 0);
console.log(result);
find() → returns first match
6. Check if All Numbers are Positive
let arr = [1,2,3];
let result = arr.every(num => num > 0);
console.log(result); // true
7. Check if Any Number is Negative
let arr = [1,2,-3];
let result = arr.some(num => num < 0);
console.log(result); // true
8. Square Only Even Numbers
Input:
[1,2,3,4]
Output:
[4,16]
Solution:
let arr = [1,2,3,4];
let result = arr
.filter(num => num % 2 === 0)
.map(num => num * num);
console.log(result);
Step 1: filter → Step 2: map
9. Count Numbers Greater Than 10
let arr = [5, 15, 20, 8];
let count = arr.filter(num => num > 10).length;
console.log(count); // 2
